1. Field of the Invention
The present invention relates to a fuel injector having a cooled lower nozzle body, and more particularly to a cooled lower nozzle body of a common rail, needle controlled injector arranged to provide for a small amount of cooling medium (fuel) to flow through the nozzle of the injector to cool the same.
2. Description of Related Art
Fuel injectors have been commonly used with internal combustion engines such as diesel engines to deliver combustible fuel to the combustion chambers within the cylinders of the engine. Various injector designs have been implemented in the art but most fuel injectors have a nozzle with a valve element movably disposed therein in which when opened, provides a spray of fuel into the combustion chamber of the cylinder. In this regard, fuel injectors typically include a nozzle including an outer barrel, a retainer, and a nozzle housing that houses the valve element of the fuel injector. The fuel injector is typically mounted to an injector bore in the cylinder head of the internal combustion engine and the nozzle housing having an injection hole generally extends at least partially into the combustion chamber so that fuel may be provided therethrough. In this regard, the retainer is received within the injector bores of the cylinder head and includes an opening proximate to the combustion chamber of the cylinder which allows the nozzle housing to extend into the combustion chamber. Such nozzle designs are generally illustrated in U.S. Pat. No. 5,441,027 to Buchanan et al.
The lower section of the nozzle outer body of an injector, or injector tip, is generally exposed to high temperatures in the combustion chamber of the cylinder during combustion. It is not uncommon for flame temperatures in the cylinder to exceed 4000° F. In such situations, the nozzle outer body can experience service temperatures in excess of its tempering temperature, for example 450° F.
In the process of normal diesel fuel injection, the fuel itself, which is in a pressurized state located in an annular cavity around the needle, serves as the media which cools the injector and the tip of the nozzle shank as the pressurized fuel is sprayed from the injector hole. However, recently there has been a tremendous push to increase fuel efficiencies and reduce emissions in internal combustion engines, and in particular, in diesel engines. In a quest to attain these goals in which the injectors and the fuel systems operation must be optimized, engineers have utilized fuel injectors which provide reduced injection flows such as in pilot injection, pre-injection, and/or through the use of a second injector. In many such applications, the quantity of fuel injected is relatively small i.e., less than 5 mm3/stroke. The cooling provided by such small quantities of fuel is insufficient to cool the tip of the nozzle. For example, when the injector is used for pilot injection, pre-injection, and/or through the use of a second injector, the mode of providing for heat transfer between the lower part of the nozzle outer body and the injection fluid is limited. Consequently, heat deformation of the nozzle tip and fuel coking, a condition created by fuel being exposed to reducing conditions, i.e., oxygen conditions which lead to carbon buildup, can occur as a direct result of insufficient cooling.
Moreover, with the advent of increased emissions regulations, alternative fuels and blends thereof have been pursued to provide alternative combustible fuels that may be used in various internal combustion engines such as modified diesel engines. However, such alternative fuels have different burn temperatures and characteristics, and certain fuels such as natural gas has a tendency to burn with a combustion flame which is positioned closer to the tip of the nozzle thereby exposing the tip of the nozzle to much higher temperatures than those experienced during normal diesel fuel combustion.
There have been various devices and methods proposed for reducing the temperature of the tip of the nozzle tip during operation of the internal combustion engine. For example, Australian Patent No. 204195 discloses an injector including a joint tightening cone with a central opening to receive the nozzle housing therethrough. The tightening cone is made of a different material than that of the nozzle and one which has good heat conduction, such as aluminum or copper. During operation of the internal combustion engine, the cone expands to tightly contact the nozzle shank of the nozzle housing thereby preventing heating of the nozzle tip that may be caused by entrance of combustion gases at the interface of the cone and the nozzle shank. The reference further discloses that favorable heat transmission conditions from the nozzle tip to the cooled cylinder head are provided via the cone. One disadvantage of such a design is that it requires a cone having a material composition different than the rest of the injector, which may increase manufacturing costs and further complicate the operation of the injector due to the differing expansion and contraction characteristics of the cone as compared to various other components of the injector.
In another approach, U.S. Pat. No. 5,860,394 discloses an injector having a nozzle tip which has an approximately 45° angle tapered nozzle tip surface which abuts a heat insulator that reduces the heat conducted from the cylinder head to the injector tip and further serves as a seal against the coolant flowing around the injector. The disadvantage of this design is that it is highly sensitive to manufacturing tolerance variances and is susceptible to failure due to the reduced material thickness of the cylinder head caused by the coolant passage that must flow very close to the nozzle tip.
U.S. Pat. No. 5,765,755 assigned to the assignee of the present invention, Cummins Engine Co., and which is hereby incorporated by reference, discloses a rate shaping nozzle assembly having an electro-discharge machined (EDM) spill passage, wherein fuel is purged from the spill passage between each injection event. Some cooling of the nozzle body will occur due to the purging of the fuel to drain. However, drainage occurs at the tip of the nozzle housing limiting the cooling effect of the fuel flowing to drain.
Therefore, there exists an unfulfilled need for an improved fuel injector having a practical and cost effective manner for increasing heat transfer from the lower nozzle body of a high pressure common rail injector. In particular, there exists an unfulfilled need for such a nozzle that will dissipate heat at a fast enough rate allowing the use of current material to form the nozzle body without adverse thermal effects to the material, thus avoiding more expensive heat resistant materials. In this regard, there is an unfulfilled need for such a nozzle which avoids expensive tooling and set-up charges by enabling the use of existing nozzles without the disadvantages of the prior art designs, especially when the fuel injector is used to deliver diesel pilot injections and/or used with alternative fuels, such as natural gas.